Problem: If $a + b = -5$ and $x + y = -5$, what is $6y + 6x - b - a$ ?
$= -a - b + 6x + 6y$ $= (-1) \cdot (a + b) + (6) \cdot (x + y)$ $= (-1) \cdot (-5) + (6) \cdot (-5)$ $= 5 - 30$ $= -25$